The present invention relates to an image processing device for use in scanners, digital photocopiers, facsimiles, etc., for performing optimum processing of a picture signal scanned from a document in accordance with resolution of the picture signal.
Conventionally known is an image processing device with a particular technique used therefor, i.e. the technique of making read line density (hereinafter referred to as resolution) in a sub scanning direction variable by changing an operational speed of a document feeding apparatus or a document scanning apparatus. Employing this technique, the image processing apparatus performs a reading operation of a document image by selecting resolution in the sub scanning direction in accordance with size of a memory capacity, and performs image processing of a picture signal obtained via the reading operation of the document image.
An example of an image processing device capable of performing such processing is the one disclosed in Japanese Unexamined Patent Publication No. 114996/1993 (Tokukaihei 5-114996 published on May 7, 1993). This image processing device converts the resolution in a sub scanning direction by reading out images where either a thinning treatment or a shift of scanning speed of an optical system can be selected according to a capacity of a temporary memory means used for transferring picture signals.
Nevertheless, although it is possible with the conventional arrangement to suppress a memory capacity to remain small, a problem has arisen as to a considerable impairment of image quality of a line drawing, such as deterioration of images, and more specifically, vanishment of small letters, thin lines, etc.
An object of the present invention is to provide an image processing device which, while realizing higher operational speed and reducing a capacity, can suppress impairment of image quality of a line drawing, etc., even when resolution in a sub scanning direction is reduced.
In order to attain the foregoing object, an image processing device according to the present invention, which receives a picture signal which was read out while resolution in the sub scanning direction is converted by changing a speed of reading images, includes:
(a) a region separating section for separating the picture signal into each region in accordance with the converted resolution in the sub scanning direction; and
(b) a resolution and regional image processing section for performing image processing on the picture signal in accordance with the converted resolution in the sub scanning direction and each region separated by the region separating section.
In the foregoing structure, since the resolution in the sub scanning direction of a picture signal to be inputted to the image processing device has been converted, the resolution in the sub scanning direction differs from the resolution in a main scanning direction, i.e. a size of an image region in the main scanning direction differs from that in the sub scanning direction. In contrast, by employing the region separating section, the picture signal can be separated into each region according to the converted resolution in the sub scanning direction, i.e. the size of an image region in the sub scanning direction with respect to an inputted image. Consequently, the picture signal can be separated into each region with high accuracy, regardless of the converted resolution in the sub scanning direction.
Additionally, in accordance with the resolution in the sub scanning direction and each region of the picture signal which has been obtained with high accuracy as described above, the resolution and regional image processing section can apply optimum image processing to the picture signal.
Further, for example, when the speed of reading images is increased for a faster operational speed, the resolution in the sub scanning direction is reduced, i.e. the size of the image region for the inputted image becomes smaller in the sub scanning direction. Therefore, only a small memory capacity is required when storing the picture signal in a memory section, etc.
A faster and small capacity image processing device which can suppress impairment of image quality due to resolution conversion in the sub scanning direction with respect to the picture signal can thus be realized.
Note that, the resolution in the sub scanning direction in the above refers to read line density in a sub scanning direction.
Furthermore, it is preferable that the image processing device of the present invention has an arrangement in which:
the region separating section calculates feature parameters indicative of a characteristic of each pixel in the picture signal and carries out a correction in accordance with the resolution in the sub scanning direction with respect to a resolution dependent feature parameter of the feature parameters, which is dependent on the resolution in the sub scanning direction so as to separate said picture signal into each region using said feature parameters including the corrected resolution dependent feature parameter.
In accordance with the foregoing structure, the region separating section carries out a correction for the resolution dependent feature parameter which is one of the calculated feature parameters and which depends on the resolution in the sub scanning direction, according to a level of the resolution in the sub scanning direction, i.e. the size of a region in the sub scanning direction with respect to an image to be read out, and separates the picture signal into each region based on the feature parameters including the corrected resolution dependent feature parameter. Thus considering the level of the resolution of the read-out picture signal in the sub scanning direction, a picture signal can be separated into each region by means of a simple correction.
In this way, region separation of a picture signal can be carried out in accordance with the resolution conversion in the sub scanning direction with high accuracy with a simple correction which does not require a complicated structure. As a result, the image processing device in which impairment of image quality caused by the resolution conversion in the sub scanning direction is suppressed can be realized.
Further, it is preferable that the image processing device of the present invention may have an arrangement in which the resolution and regional image processing section is a filter processing section for selecting a filter factor in accordance with the converted resolution in the sub scanning direction and each region separated by the region separating section, and for performing filter processing with respect to each pixel in the picture signal by using the selected filter factor.
In the foregoing structure, the resolution and regional image processing section is the filter processing section for performing the filter processing with respect to each pixel, and it can select a filter factor which produces an optimum effect on the size of the resolution in the sub scanning direction and each region obtained with high accuracy by the region separating section. For example, for a character region in which characters, line drawings, etc. deteriorate in accordance with the reduction in the resolution in the sub scanning direction, a filter factor for heightening sharpness will be selected. In addition, for a mesh dot region where moirxc3xa9 becomes intense according to the reduction in the resolution in the sub scanning direction, a filter factor for raising smoothness so as to suppress moirxc3xa9 will be selected. Optimum filter processing can thus be applied to the resolution in the sub scanning direction and each region.
In this way, a quality image for each region can be acquired, and moreover, deterioration of image quality can be suppressed, even when the resolution in the sub scanning direction is changed.
Note that, the moirxc3xa9 in the above refers to an interference which is caused by an interaction between a frequency and a resolution of an image.
Additional objects, features, and strengths of the present invention will be made clear by the description below. Further, the advantages of the present invention will be evident from the following explanation in reference to the drawings.